Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as medical, automobile and other applications. Color sensitive digital imagers are well known. Typically color imagers are comprised of a plurality of image sensor pixels, each being sensitive to light of one of three different colors. For high dynamic range (HDR) image sensors, the big-small pixel scheme is often used, wherein some of the pixels are larger than others. The big-small scheme facilitates the capture of images with a higher dynamic range (HDR) and provides more details in images with widely varying local light intensities. In areas of the image with lower light intensity, the big pixels will be sampled, because they are more sensitive to the light. In areas of the image with high light intensity, the small pixels will be sampled, because they are less sensitive to the light, therefore, will be less likely to become saturated. The resultant image has a higher dynamic range, and shows more details in both high and low light areas.
In order to further improve the performance of the small pixels, an extra attenuation layer is usually disposed over the small pixels to block a portion of the light from reaching the small pixels. The attenuation layer is usually made of dark pigment material which has thickness at least 1 μm. Such thick attenuation layer may cause several problems, such as worse cross talk between adjacent pixels and non-uniform angular response between small pixels and big pixels.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.